iTunes MP3 Encoder Doesn’t Handle Poor CDs Well?

21 Feb 2003

Paul R. Potts

I’m a fan of the Lord of the Rings film soundtracks; I’ve purchased both the Fellowship and Towers soundtrack. A couple of days ago I was attempting to use TTT on a new dual-processor 867 Mhz G4 Mac running MacOS X 10.2.4. The first thing I noticed was that trying to open the MacOS volume containing the CD “extras” would kill my finder, kill iTunes, and eventually lock up the machine to the point where a hard reboot was necessary.

I’ve seen this before; the MacOS CD-ROM drivers don’t respond very well to flakey discs, and a reboot is often the only answer. For comparison, I tried mounting the same disc in an older 400 MHz G4, and it mounted fine. Ditto with my personal older 400 MHz TiBook. But, on all machines, listening to the CD resulted in a lot of skips and dropouts. There were only a few minor scratches visible, but the audio was terrible. This was not the case with the Fellowship CD, which was actually much more scratched. Unfortunately I have long since lost the receipt for TTT disc and cannot return it.

To try to salvage the situation, I attempted to encode the disc on my TiBook, whose internal drive seemed to have the best luck at reading the disc. I was disappointed to find that the MP3 encoding failed badly, although it worked a little better than it had on the new G4. Hoping to get a clean listenable copy of “Gollum’s Song,” given that I had paid for the disc, I tried again using the AIFF encoder.

To my surprise the AIFF encoder chugged away and seemed to produce a much better rip, with no pops, skips, or dropouts. It tortured the drive: I could hear the drive scrambling back and forth, perhaps re-reading bad data in an attempt to correct errors. It seems to be the case that the AIFF encoder does its best to re-read the disc when it encounters errors, but the MP3 encoder does not. Could this be the case? Or does the AIFF encoder just do better interpolation to hide errors?

In any case, I found that the path to get a listenable MP3 encoding was to encode the whole disc to AIFF at native quality, then write an audio CD from the AIFF rip, then re-MP3-encode the resulting audio CD. This long and stupid procedure seems to have completely salvaged the situation and I have a listenable copy of the Two Towers soundtrack now. The audio quality emerging from the Mac headphone jack is not sufficient for me to hear whether this has truly repaired the situation; there seems to be some distortion on parts of Gollum’s song, but it is bearable. I should try listening to the CD burned from AIFFs on a conventional CD player to determine what kind of job it did.

No profound lesson here, except I’m left wondering if the MP3 encoder could be improved with the addition of some better error-handling code, and also left musing on how if I was not able to so easily attempt various methods of encoding and burning this music I’d be left holding an unusable copy of a CD I paid good money for. One could speculate about this quality control, although I have not heard reports of a high defect rate. It brings home to me again just how fragile CDs are and the need for a more robust medium.

Followup 23 Mar 2004: It appears that more recent versions of iTunes have an option to use error correction when importing audio CDs. The preferences dialog notes that this may reduce the speed of importing. That’s far preferable (to me, at least) than ignoring bad audio data.

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